Don't mess with Tim Robbins's family values. The actor and director wound up firing off expletives at a Washington Post gossip columnist at the Vanity Fair Oscars after-party once he learned that the writer had written an expose of longtime partner Susan Sarandon's political family rift.

The backstory: Sarandon, 56, and Robbins, 45, are outspoken liberals who drew flashbulbs at the Oscars ceremony by waving peace signs at the audience. But as a recent Post story noted, Sarandon mom Lenora Tomalin is a conservative Republican and George W. Bush backer; the earlier Post story had quoted Floridian Tomalin as saying the couple had politically "brainwashed" their son, Jack Henry, over the results of the 2000 election.

Fast-forward to Sunday night, and Robbins was apparently all smiles -- until he learned that columnist Lloyd Grove was the one who'd interviewed his mother-in-law. "Wait. You're the one who wrote about Susan's mother?" the actor queried -- narrowing his eyes and pursing his lips, according to Grove.

"You wanted to be divisive, and you caused trouble in my family," Robbins continued. ".... If you ever write about my family again, I will (bleeping) find you and I will (bleeping) hurt you."